In recent years, a cellular phone of a multi-band system that mounts transmitting-receiving systems of multiple communication systems in a single cellular phone, and can select them in accordance with regional characteristics and purposes for use is introduced. The cellular phone of the multi-band system must be provided with a transmitting-receiving circuit of each communication system and a branching circuit that branches a frequency band of the communication system. If each component is mounted individually, however, the cellular phone is made large, and leads to being increasingly expensive.
Concerning this type of problem, for example, a multi-band transceiver shown in Japanese Patent Laid-Open No. 2003-8470 (USP2002-196085) is disclosed. This multi-band transceiver integrates a branching circuit, a switching circuit that switches the transmitting-receiving circuit of each communication system, a power amplifier for amplifying a transmitted signal, and a coupler for monitoring the output of the power amplifier. The multi-band transceiver forms a matching circuit unit of the branching circuit, the switching circuit, the coupler, and the power amplifier in a dielectric substrate, and mounts diodes or elements of an amplifier circuit of the power amplifier on this substrate. Consequently, a high frequency circuit unit of the multi-band cellular phone is miniaturized and realizes cost reduction.
The multi-band cellular phone of JP-B No. 8470/2003, however, is limited to a communication system, such as a GSM (global system for mobile communications) or a DCS (digital cellular system) according to TDMA (time division multiple access), and cannot be used in the communication system including CDMA (code division multiple access).
To realize a multi-band transceiver that can be used in the multi-band cellular phone including the CDMA, the switching circuit unit of the aforementioned multi-band transceiver can be replaced by an antenna shared device consisting of a matching circuit between a transmitting filter, a receiving filter, and a filter. Usually, a SAW filter is used here as the transmitting filter or the receiving filter.